let arr = [
  {
    start: '04:00',
    end: '08:00',
    createTime: null
  },
  {
    start: '08:00',
    end: '10:00',
    createTime: null
  },
  {
    start: '10:00',
    end: '12:00',
    createTime: null
  }
]

// let str = JSON.stringify(arr)
// console.log(str);
// let arr1 = JSON.parse(str)
// console.log(typeof (str));
let arr1 = [1, 2, 3]
console.log(JSON.stringify(arr1));